Automatic defrost control for refrigeration systems



July 16, 1963 J. LIEBERMANN 3,097,503

AUTOMATIC DEFROST CONTROL FOR REFRIGERATION SYSTEMS Filed Dec. 15, 1961INVENTOR JOHN LIEBERMANN ATTORNEY United States Patent 3,097,503AUTOMATIC DEFRUST (ZONTROL FUR REFRIGERATION SYSTEMS John Liebermann,Columbus, Ohio, assignor to Rance Incorporated, Columbus, Ohio, acorporation of @2320 Filed Dec. 13, 1961, Ser. No. 159,126 5 Claims.((31. 62156) This invention relates to improvements in automatic controlmeans for electric motor driven mechanical refrigerating systems of thecompressor-condenser-expander type in which defrosting of the evaporatorof the system is effected at the beginning of each refrigerating cycle.

It is a principal object of this invention to provide improved controlmeans in a refrigerating system of the compressor-condenser-expandertype having a cycling thermostatic switch for controlling operation ofthe compressor to produce refrigerating cycles and an electricallycontrolled valve which may be opened upon energization thereof to passhot compressed refrigerant directly from the compressor to theevaporator to effect removal of frost therefrom, the control of thevalve being effected by circuit means including a switch in series withthe cycling thermostatic switch, the valve control switch beingthermostatically operated to close upon a reduction in temperature ofthe evaporator below a given temperature and to open upon a rise intemperature of the evaporator above the melting point of frost toterminate passage of hot gas through the evaporator, and means toprevent reenergization of the valve as long as the compressor is inoperation and irrespective of the reduction in temperature of theevaporator.

Another object of this invention is the provision of an improvedrefrigeration control system of the above mentioned character whereinthe defrosting, or valve control switch is preferably operated bythermally responsive means such as a bellows connected to a bulb locatedat the evaporator, the defrosting switch means having two operativepositions one of which connects the electrically operated valve inseries with the cycling thermostatic switch so that the valve isenergized and opened to commence defrosting when the compressor isstarted by the cycling thermostat, the defrosting switch means beingmoved by the resulting increase in temperature in the evaporator to apredetermined temperature above 32 F. to its second operative positionto break the circuit of the valve, thereby allowing the valve to closeand establish the cooling cycle and to energize means for preventingreenergization of the defrost valve until the cycling thermostat hasterminated the refrigerating cycle. In. one preferred form of theinvention the means for preventing reenergization of the defrostingvalve comprises a relay switch in the circuit between the defrostingswitch means and the valve, the relay being effective, when energized,to prevent energization of the valve and having a holding circuitincluding the cycling thermostat switch, so that although the defrostingswitch means be returned to its valve energizing position, the relaywill remain energized and prevent reenergizing and opening of thedefrosting valve until. the cycling thermostat switch has opened tobreak the holding circuit.

Other objects and advantages of this invention will become apparent,from the following detailed description of a presently preferredembodiment thereof described with reference to the accompanying sheet ofdrawings forming a part of this specification, and in which the singleview provides a schematic illustration of a refrigerating systemembodying the present invention.

The present invention is described hereinafter with reference toembodiment in a mechanical refrigerating system generally indicated at19, such as may be used in domestic refrigerators, although it will beunderstood that ice this use is intended only as an example and that theinvention may be embodied in similar cooling systems for use incommercial freezers, coin operated vending units, an conditioningsystems for habitable buildings, and the like. Refrigerating system 10comprises a compressor 13 which is driven by a prime mover such as anelectric motor 14 and is operative to withdraw vaporized refrigerantthrough a tube 15 from a cooling unit or evaporator 16, and to compressthe refrigerant and direct it through. a tube 17 to a condenser 18.

The refrigerant is cooled and liquified in condenser 18, from which thecondensed refrigerant is led by a tube 20 through a suitable expansionmeans, such as a capillary tube 21, into the evaporator 16 where therefrigerant vaporizes and cools the walls of the evaporator, as is wellunderstood in the art. Motor 14 is connected by conductors 24, 25, and acompressor cycling thermostatic switch 26 to power lines L1 and L2.Thermostatic switch 26 is responsive to temperatures in the refrigeratorcompartment, or other space being tempered by the cooling effect of theevaporator 16, and is adapted to energize and deenergize motor 14 tostart and stop the compressor to produce refrigerating cycles as may benecessary to maintain the compartment temperature within predetermineddesired limits.

When the evaporator is operated at temperatures below the freezing pointof water, moisture in the air surrounding the evaporator is condensedand frozen on the surface of the evaporator in the form of frost.Because accumulations of such frost act as an insulation between theevaporator and the surrounding air, the efficiency of the refrigeratingsystem would be impaired if the frost were permitted to remain. In therefrigerating system shown, however, such frost is melted at thebeginning of each refrigerating cycle, and for this purpose an electricsolenoid actuated, normally closed valve 30 is connected between tubes17 and 22 by tubes 31 and 32, and hence is adapted to provide a path fordirecting hot compressed refrigerant coming from the compressor 13;directly into evaporator 16 so as to raise the temperature thereof toremove formations of ice and frost therefrom. Valve 39 may be of anywell known type such as asolenoid operated valve of the type disclosedin my copending patent application Serial Number 8,3 3 6- filed February12, 1960; Valve 30 is actuated to an open condition each time thethermostatic switch 26 closes to start compressor 13 for a refrigeratingcycle, and is heldopen by control means, described more fully as thedescription proceeds, until the evaporator has attained a temperature atwhich the frost is. melted. Thereafter, the valve is closed and theevaporator is cooled in the normal manner until thermostatic switch onceagain opens.

The control means for valve 30 includes: a thermally responsivedefrosting switch, generally indicated at 34, and a relay 35. Switch 34may be of any single pole, double throw, snap acting type well known inthe art, and is here shown as comprising a movable contact arm 36 whichis fixed at one end and carries adouble contact 31 at its movable end.Contact 37' is movable between spaced staionary contacts 38 and 39 witha snap movement effected by a toggle mechanism including a bowed tongue40, struck out of the center of arm 36 and having a free: end engaged ina notch 41 of a toggle member 42 which is pivoted at 43 to a suitableframe 44. It willbe recognized that movement of toggle member 42 in acounterclockwise direction from its illustrated position so as to bringnotch. 41 to the other side of arm 36, will cause the latter to besnapped upwardly to bring contact 37 into engagement with contact 38.Conversely, movement of toggle member 42 in a clockwise direction so asto bring notch 4 .1 past arm 36, will cause. contact 37 to be returnedinto engagement with contact 39 with a snap action.

A compression spring 46 is disposed between toggle member 42 and frame'44, and biases toggle member 42 in a counterclockwise direction aboutpivot 43. An expansible power member in the form of a bellows 487ismounted on frame 44 and has a post 49 in engagement with toggle member42. Bellows 48 is connected by a capillary tube 50 with a temperaturesensing bulb 51 disposed adjacent evaporator 16. Bulb 51 contains avolatile liquid, such as Freon which is in a liquid state for the normaltemperatures encountered during operation of the refrigerating system sothat the vapor pressure corresponds to the lowest temperature of thethermostatic system, which is generally the bulb 51. Such changes inpressure are transmitted by capillary tube 50 to bellows 48 to effectexpansion and contraction thereof, through the action of spring 46, andactuation of the toggle mechanism so as to move contact 37 intoengagement with contact 39 as shown in the drawing. The force exerted byspring 46 is such that when the temperature of evaporator 16 is reducedbelow the freezing point of water the reduction in pressure in thebellows permits the spring to depress bellows 48 and thereby shiftcontact 37 to engage contact 38.

Relay 35 which cooperates with switch 34 to control actuation of valve30, comprises a solenoid 53, normally closed contacts 54, and normallyopen contacts 55. Assuming the refrigerating apparatus to have bee-nstanding idle and to be entirely at room temperature, the various partsof the refrigerating system would be positioned as shown in the drawing.Upon supplying lines L1 and L2 with current such as 110 v. A.C., motor14 is energized to start operation of compressor 13 as previouslydescribed, and the temperature of evaporator 16 is brought to atemperature somewhat below freezing. As evaporator :16 passes into thefreezing temperature zone, switch 34 is actuated to bring contacts 37into engagement with contact 38, or into what will hereafter be referredto as the first operative position of this switch. When the refrigeratorhas been suificiently cooled, thermostatic switch 26, which is shownschematically as a bimetal switch, opens to deenergize motor 14 andterminate the first refrigerating cycle and also deenergizes relaysolenoid 53 to cause reclosing of switch 54 and reopening of switch 55.

At the initiation of every subsequent refrigerating cycle, defrostingvalve 30 will be opened to direct hot gas into evaporator 16 to removefrost therefrom. Thus, when the refrigerator temperature risessutficiently to close thermostatic switch 26 for energization ofcompressor motor 14, a circuit is closed which may be traced fromconductor 25 through conductors 60, 61, arm 36, now closed con tacts 37and 38, conductor 63, normally closed contacts 54 of relay 53, conductor64, electrically operated defrosting valve 30, and a conductor 65 toline L2. Valve 30 is therefore energized and opened to commence thedefrosting action. When evaporator 16 attains a predeterminedtemperature which will assure the removal of frost therefrom, the liquidin bulb 51 is vaporized causing expansion of bellows 48 and actuation ofswitch 34 from its first operative position to a second operativeposition by snapping contact 37 from contact 38' to contact 39.

Opening of contacts 37 and 38 interrupts the energization of valve 38which therefore closes to terminate defrosting of the evaporator and topermit the commencing of the cooling portion of the cycle. Closing ofcontacts 37 and 39 completes a circuit including conductors 60, 61, arm36, now closed contacts 37 and 39, solenoid 53, and a conductor 67 toline L2. Relay 35 is thereby actuated causing contacts 54 to open andcontacts 55 to close. Closing of contacts 55 establishes a holdingcircuit for relay 35, which circuit may be traced from conductor. 60through conductor 68, contact 55, a conductor 69, solenoid 53, andconductor 67 to line L2. This holding circuit maintains relay 35energized even though switch 34 is then actuated to its first operativeposition (opening contacts 37 and 39) as the evaporator is reduced to atemperature below freezing during the remainder of the refrigeratingcycle. Because relay 35 remains energized, contacts 54 are held open andprevent the reopening of valve 30 upon closing of contacts 37 and 38.

When the cooling eflects of the evaporator 16 reduce the temperaturewithin the refrigerator sufliciently to open thermostatic switch 26, theholding circuit for relay 35 is broken allowing contacts 55 to open andcontacts 54 to close. Switch 34 and relay 35 are therefore conditionedto energize valve 30 once again upon the next closing of thermostat 26to initiate another refrigerating cycle. The above described sequence ofevents, including the operation of switch 34 and relay 35 to open valve30 at the beginning of each refrigerating cycle, is continuouslyrepeated, thereby maintaining evaporator 16 free of frost and at peakefiiciency.

Inasmuch as evaporator 16 and bulb 51 are, during defrosting, raised toa temperature somewhat above that in the remainder of the refrigerator,a small electrical resistance heater 71 is disposed adjacent capilliary50 and bellows 48 so that bulb 51 will always be the coldest part of thevolatile liquid containing system. This is necessary since such a systemis responsive only to temperature changes in the coldest portionthereof, as is well understood by those skilled in the art to which theinven tion pertains. Heater 71 is conveniently energized by connectionbetween conductor 61 and line L2 by conductors 72 and 73, as shown.

From the foregoing detailed description of a presently preferredembodiment of the invention, it will be recognized that there has beenprovided thereby a particularly effective refrigerator control systemwhich maintains the evaporator substantially free of frost by effectinghot gas defrosting upon the initiation of each refrigerating cycle. Itwill also be recognized that the invention may be practiced by theutilization of relatively simple and reliable components such asswitches and relays which are inexpensive and require little or noadjustment other than that performed at the factory upon fabrication.

Although the invention has been described in considerable detail andwith specific reference to a refrigerating system embodying theinvention, it is understood that the invention is not limited thereto,but rather the invention includes all those changes, modifications, anduses as are reasonably embraced by the scope of the claims hereof.

Having thus described my invention, I claim:

1. In a refrigerating system comprising:

(a) a cooling unit,

(b) an electrically powered means to circulate refrigerant through saidunit,

(0) a thermostatically operated first switch controlling saidelectrically powered means according to temperatures effected by saidcooling unit,

(d) electrically powered valve means to selectively direct a fluid ofrelatively high temperature through said cooling unit to melt frosttherefrom,

((2) means to control said electrically powered valve means comprising acircuit connecting said valve means in series with said first switch,

(1) a second switch in said circuit in series with said valve,

(g) thermostatic means responsive to the temperature of said coolingunit and operative to close said second switch in response to a decreasein temperature below a given temperature and open said second switch inresponse to an increase in temperature of said cooling unitsubstantially above 32 F., to deenergize said valve, and

(h) means responsive to opening of said second switch during anoperating cycle of said refrigerant circulating means to maintain saidvalve deenergized for the remainder of said opera-ting cycle and untilthe beginning of the next cycle irrespective of the reduction intemperature of said evaporator and closing of said second switch duringsaid remainder of said operating cycle.

2. Control means in a refrigeration system of the type including acompressor, a prime mover for said compressor, a condenser and anevaporator connected to said compressor to form a closed path forrefrigerant, and an electrically operated valve for directing hot gasfrom said compressor to said evaporator to effect defrosting thereof;said control means comprising:

(a) a first thermally responsive switch means for start ing and stoppingoperation of said compressor by said prime mover,

(b) a second thermally responsive switch means connected in series withsaid first switch means and with \said electrically operated valve sothat said valve is opened when both switches are closed,

(c) said second switch being adapted to open in response to atemperature rise in said evaporator to a predetermined defrostingtemperature whereby said valve is closed and cooling of said evaporatorstarted, and

(d) electrically actuated means for preventing said second switch fromeffecting reopening of said valve upon a decrease in temperature of saidevaporator until the next opening and closing of said first switchmeans.

3. Control means in a refrigeration system of the type including acompressor, a prime mover for said compressor, a condenser and anevaporator connected to said compressor to form a closed path iorrefrigerant, and an electrically operated valve for directing hot gasfrom said compressor to said evaporator to effect defrosting thereof;said control means comprising:

(a) a first thermally responsive switch means for starting and stoppingoperation of said compressor by said prime mover,

(b) a second thermally responsive switch means having a first operativeposition connecting said valve to said first switch means so thatclosing of said first switch means to start .said compressor will alsoeffect opening of said valve to effect defrosting,

(c) said second switch means being responsive to attainment of apredetermined defrosting temperature of said evaporator to shift fromsaid first operative position to a second operative position and toeffect closing of said valve,

(d) electrically actuated holding means connected in series with saidfirst switch means and operative to prevent said second switch meansfrom effecting reopening of said valve upon reduction of said evaporatortemperature below said predetermined temperature until the next openingof said first switch means to release said holding means.

4. Control means in a refrigeration system of the type including acompressor, a prime mover for said compressor, a condenser and anevaporator connected to said compressor to form a closed path forrefrigerant, and an electrically operated valve for directing hot gasfrom said compressor to said evaporator to effect defrosting thereof;said control means comprising:

(a) a first thermally responsive switch means for starting and stoppingoperation of said compressor by said prime mover,

(b) a second thermally responsive switch means having a first operativeposition connecting said valve to said first switch means so thatclosing of said first switch means [to start said compressor will alsoeffect opening of said valve to effect defrosting,

(c) said second switch means being responsive to attainment of apredetermined defrosting temperature of said evaporator to shift firomsaid first operative position to a second operative position and toeffect closing of said valve,

(d) electrically actuated holding means connected in series *with saidfirst switch means and operative to prevent said second switch meansfrom effecting reopening of said valve upon reduction of said evaporatortemperature below said predetermined temperature and until the nextopening of said first switch means which is operative upon said nextopening to release said holding means,

(2) said electrically actuated holding means comprising a relay havingcontacts connected between said second switch means and said valve, saidrelay being actuated to open said contacts and hence to close said valveupon movement of said second switch means from said first operativeposition to said second operative position, and said relay havingholding means to prevent reclosing of said contacts until said nextopening of said first switch means.

5. Control means as defined in claim 4 and wherein said holding meanscomprises an electrical holding circuit through second contact means ofsaid relay.

References Cited in the file of this patent UNITED STATES PATENTS

2. CONTROL MEANS IN A REFRIGERATION SYSTEM OF THE TYPE INCLUDING ACOMPRESSOR, A PRIME MOVER FOR SAID COMPRESSOR, A CONDENSER AND ANEVAPORATOR CONNECTED TO SAID COMPRESSOR TO FORM A CLOSED PATH FORREFRIGERANT, AND AN ELECTRICALLY OPERATED VALVE FOR DIRECTING HOT GASFROM SAID COMPRESSOR TO SAID EVAPORATOR TO EFFECT DEFROSTING THEREOF;SAID CONTROL MEANS COMPRISING: (A) A FIRST THERMALLY RESPONSIVE SWITCHMEANS FOR STARTING AND STOPPING OPERATION OF SAID COMPRESSOR BY SAIDPRIME MOVER, (B) A SECOND THERMALLY RESPONSIVE SWITCH MEANS CONNECTED INSERIES WITH SAID FIRST SWITCH MEANS AND WITH SAID ELECTRICALLY OPERATEDVALVE SO THAT SAID VALVE IS OPENED WHEN BOTH SWITCHES CLOSED, (C) SAIDSECOND SWITCH BEING ADAPTED TO OPEN IN RESPONSE TO A TEMPERATURE RISE INSAID EVAPORATOR TO A PREDETERMINED DEFROSTING TEMPERATURE WHEREBY SAID